Technical Abstract:
In calves, efficient nutrient delivery, absorption, and metabolism depend upon the transition of the rumen from a pre-ruminant to a true ruminant state during weaning. The rumen epithelium is responsible for several physiologically important functions, including absorption, transport, volatile fatty acid metabolism, and protection. In contrast to other service function organs, which decline as a percentage of empty body weight as the ruminant matures, the rumen increases from 30 to 70% of the capacity of the gut during the weaning process. Thus, this tissue plays a central role in dictating the net efficiency of feed conversion. To identify genes controlling development and differentiation of the calf rumen, 18 Holstein bull calves were assigned randomly to dietary treatments of either commercial milk replacer only (milk), milk + hay, or milk + grain (commercial calf starter). Calves fed milk only were sacrificed at either day 14 (n = 3) or day 42 (n = 3) of life. Calves fed milk + hay or milk + grain were fed milk replacer only until day 42 of life (weaning) and then were provided either milk + hay or milk + grain thereafter and sacrificed on day 56 (n = 3) or day 70 (n = 3) of life. Rumen epithelial tissue was collected from each calf at slaughter for RNA extraction and transcript profiling was conducted by microarray hybridization using a whole genome bovine array.